1. Field of the Invention
The present invention relates to fluid filtering systems and, more particularly, to fluid filtering systems that produce agglomeration of particles in the fluid by means of a plurality of electrically charged panels such as electrets, metals, conductive materials or electrically charged materials.
2. Technical Background
Efforts have been made to create electrically charged dust filters to capture particles because of the associated high initial efficiencies. Such devices, commonly referred to as electrical precipitators, use pairs of charged plates of opposing charges, each creating a separate zone of influence over the passing particles. The first zone has the purpose of imparting a charge in the fluid by means of ionizing the fluid with the use of grids, panels, or plates that are electrically charged. The particle being transported through this zone by the fluid becomes charged. A second plate or grid downstream creates a capture zone. It is charged with an opposing charge. This opposing charge attracts the particles and causes them to attach to the capture plates or grids. This deposition and accumulation of particles on the plates produces unacceptable maintenance problems associated with a rapid drop in efficiency of the filtering process as the capture plate gets dirty. Furthermore, present day electrically charged filter systems have limited use because plate cleaning systems, other than manual methods, are generally expensive and subject to high maintenance costs, requiring an inordinate amount of cleaning to maintain claimed efficiencies. These electrically charged filter systems have a complicated expensive construction due to the design and expected reliability of operation.
It is known that certain materials can be permanently electrically charged, such as by heating the material, applying a high-voltage electrical field, and cooling the material while under the influence of the electrical field. These materials form an electret when the rate of decay of the field-induced polarization can be slowed down so much that a significant fraction of the electrical charge is preserved long after the polarizing field has been removed. Such electrets with a sustained or permanent electrical charge can be made by various methods, e.g. corona charging, triboelectrical charging (friction) and so forth. To improve the charge within an electret, various topical treatments have been used as a means to improve the stability of such charges. In addition, electret non-woven webs of non-polar polymeric materials have been provided which introduce polar groups onto side-chains and/or the backbone of the non-polar monomer or otherwise grafting unsaturated carboxylic acids thereon. Such electret materials have been used to form filters to trap particles in the air or other fluids.
The use of electret devices to produce agglomeration of particles in a fluid would greatly improve the process of electrical filtration by providing a safe and inexpensive means of removing particles from air and other fluids. However, such devices have heretofore been unknown.